I. Field of the Invention
The present invention relates to a stereoscopic apparatus and method for producing images that can be displayed as three-dimensional illusions and more particularly to an autostereoscopic imaging apparatus and method for producing images that, on display, can be perceived to be three-dimensional without the use of special viewing aids.
II. Prior Art
The production of two-dimensional images that can be displayed to provide a three-dimensional illusion has been a long standing goal in the visual arts field. Methods and apparatuses for producing such three-dimensional illusions have to some extent paralleled the increased understanding of the physiology of human depth perception.
Binocular (stereo) vision requires two eyes to view a scene with overlapping visual fields. Each eye views a scene from a slightly different parallax angle and focuses the scene unto a retina. The two-dimensional retinal images are transmitted by optic nerves to the brain's visual cortex, where they are combined, in a process known as stereopsis, to form a three-dimensional model of the scene.
Depth perception of three-dimensional space depends on various kinds of information (cues) perceived from the scene being viewed, such as relative size, linear perspective, interposition, light and shadow, gradients (monocular cues), as well as retinal image size, retinal disparity, accommodation, convergence (binocular cues), and familiarity with the subject matter of the viewed scene (learned cues).
Retinal disparity, which is the separation between a person's eyes, provides parallax information. It is now well known that depth perception can be achieved when left and right eye depth information is presented alternately to the brain, as long as the time interval does not exceed 100 milliseconds. It has been demonstrated that the brain can extract parallax information from a three-dimensional scene even when the eyes are alternately covered and uncovered for periods up to 100 milliseconds each. The brain can also accept and process parallax information presented to both eyes if sequenced properly. The ideal view cycle sequencing rate has been determined to be between 3-6 Hz.
True three-dimensional image displays can be divided into two main categories, stereoscopic or binocular and autostereoscopic. Stereoscopic techniques (including stereoscopes, polarization, anaglyphic, Pulfrich, and shuttering technologies) require the viewer to use a viewing device, such as polarized glasses. Autostereoscopic techniques, such as holography, lenticular screens, parallax barriers, alternating-pairs and parallax scans produce images in a true three-dimensional illusion without the use of special viewing glasses.
Prior art autostereoscopic television and motion picture systems have utilized the approach of alternately displaying views of a scene recorded by two cameras from different points of view. U.S. Pat. No. 4,006,291 to Imsand; U.S. Pat. Nos. 4,303,316 to McElveen; U.S. Pat. No. 4,429,328 to Jones et al.; U.S. Pat. No. 4,966,436 to Mayhew & Prichard, all utilized two cameras to record horizontally, vertically, or a combination of horizontally and vertically displaced views of a scene. While this autostereoscopic approach produces images which provide three-dimensional illusion when displayed, precision matching of the two cameras is required. Improper alignment of the cameras, lens mismatches in focal length and/or focus, chrominance and illuminance mismatches, and misplaced convergent points all contribute to image instability. Also, considerable operator skill is required to continuously adjust disparity, convergence and time-displacement rates of image recordings in a coordinated manner to maintain a stable image.
Image stability can be rendered less noticeable by the use of masking techniques. Camera motion is very effective in hiding rocking motions of images, apparently because the brain places less importance on rocking motion than on camera motion. This could result from some sort of natural stabilizing phenomena or mechanism of the brain that allows us to see clearly while walking or running, when images would otherwise bounce.
To avoid the drawbacks associated with a two-camera autostereoscopic system, autostereoscopic methods and apparatuses using a single camera/single lens have been developed. Mayhew et al. U.S. Pat. Nos. 5,014,126 and 5,157,484 disclose single camera autostereoscopic systems capable of recording images which, when displayed, are perceived by a viewer in three-dimension. Commonly assigned, copending U.S. patent application No. 08/115,101, filed Sep. 2, 1993 by Fernekes et al. discloses a method and apparatus, wherein a single camera records images while undergoing oscillatory parallax scanning motion.
While the single camera autostereoscopic imaging systems disclosed in the above cited prior art are effective in producing high quality, stable images that can be perceived in three-dimension when viewed with the unaided eye, unfortunately the apparatuses are rather bulky and heavy, relatively complex in construction, and consume a meaningful amount of power in operation.